1. Field of the Invention
The present invention relates to high frequency modules for transmitting and receiving transmission and reception signals of at least four communication systems having different frequency bands as transmission and reception bands through a single antenna.
2. Description of the Related Art
Currently, multiple wireless communication systems for mobile phones, such as a CDMA system and a TDMA system, exist. The TDMA system includes for example, a GSM system using an 850 MHz band and a 900 MHz band, a DCS system using a 1,800 MHz band, and a PCS system using a 1,900 MHz band, whereas, the CDMA system includes, for example, a WCDMA system using a 2,000 MHz band.
When transmitting and receiving such multiple types of communication signals with a single antenna, the signals other than those in the frequency band used for the actual communication is not needed. For example, when carrying out transmission and reception using the GSM system (900 MHz band), the communication signals for the DCS system (1,800 MHz band) and the PCS system (1,900 MHz) and the communication signals for the WCDMA system (2,000 MHz) are not needed.
As a high frequency module for transmitting and receiving multiple types of communication signals through a single antenna when the communication signals are according to, for example, three types of systems, GSM, DCS, and PCS, a high frequency module including a diplexer for separating the GSM communication signals and the DCS and PCS communication signals that are in significantly different frequency bands, a diode switch circuit for switching between the GSM transmission signals and the GSM reception signals, a diode switch circuit for switching between the DCS and PCS transmission signals and the DCS and PCS reception signals, and a diode switch circuit for switching between the DCS reception signals and the PCS reception signals has been proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2000-165288).
As such a high frequency module for transmitting and receiving multiple types of communication signals through a single antenna, a high frequency module capable of selecting each communication signal using a semiconductor switch, such as a GaAsIC switch and switching the connection between a plurality of ports for an antenna has been proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-160724).
However, the diode switch circuit for the high frequency module according to the above-mentioned Japanese Unexamined Patent Application Publication No. 2000-165288 uses two diodes to switch between two ports (input unit and output unit) corresponding to one port (input and output unit). For example, according to Japanese Unexamined Patent Application Publication No. 2000-165288, the diode switch circuit (high frequency switch 3 shown in a drawing of Japanese Unexamined Patent Application Publication No. 2000-165288) switches the connection between a port that connects to a diplexer and inputs and outputs DCS and PCS transmission and reception signals, and a port that connects to a PCS and DCS transmission signal input terminals and inputs DCS and PCS transmission signals or that connects to another diode switch circuit (high frequency switch 4 shown in a drawing of Japanese Unexamined Patent Application Publication No. 2000-165288) and outputs DCS and PCS reception signals. The diode switch circuit (high frequency switch 4 shown in a drawing of Japanese Unexamined Patent Application Publication No. 2000-165288) is connected to another diode switch circuit (high frequency switch 3 shown in a drawing of Japanese Unexamined Patent Application Publication No. 2000-165288) and switches the connection between and a port for inputting DCS and PCS reception signals and a port for outputting a PCS reception signal connected to a PCS reception signal output terminal or a port for outputting a DCS reception signal connected to a DCS reception signal output terminal. Since, in this way, the high frequency module according to Japanese Unexamined Patent Application Publication No. 2000-165288 requires at least two diodes to switch the connection between one port and two ports, many circuit components are required to construct a high frequency module for switching between transmission and reception of communication signals of a plurality of communication systems.
Therefore, it is difficult to reduce the size of the high frequency module, and costs increase because of an increase in the number of components. Since, in this way, many circuit elements are connected to the transmission system, the loss of the transmitted signal increases. Since the loss significantly increases as the number of types of the communication system for transmitting the signal increases, it is difficult to construct a high frequency switch for switching the transmission of signals of many different types of communication systems so that the high frequency switch has low loss.
On the other hand, since the high frequency module according to Japanese Unexamined Patent Application Publication No. 2001-160724 is capable of switching signals of many types of communication systems using one GaAsIC switch, a small-size, low-loss high frequency module is realized. However, GaAs is expensive, and, in particular, the price increases as the number of switching points of a GaAsIC increases since the scale of the circuitry increases. Moreover, GaAs is susceptible to static electricity. Therefore, when using such an IC, a separate circuit must be provided as a counter measure against static electricity. As a result, if a high frequency module is constructed using a multipoint GaAsIC for switching signals of many types (for example, more than four types) of communication systems, cost significantly increases and size cannot be decreased because an additional circuit is required.